1. Field of Invention
The present invention relates to a bi-directional switching regulator and a control circuit of the bi-directional switching regulator; particularly, it relates to such bi-directional switching regulator and control circuit capable of effectively controlling the charging current to prevent the circuit from being crashed and the battery from being damaged.
2. Description of Related Art
Please refer to FIG. 1, which shows a schematic diagram of a conventional bi-directional switching regulator. The bi-directional switching regulator 10 can operate under a power supply mode (a discharging mode) or a charging mode. When the bi-directional switching regulator 10 is under the charging mode, it conducts a boost power conversion and converts an input voltage VBUS to an output voltage VSYS. That is, the bi-directional switching regulator 10 converts the lower input voltage VBUS to the higher output voltage VSYS. In this case, the input terminal BUS supplying the input voltage VBUS can be connected to an external power source. The output terminal SYS generating the output voltage VSYS can be connected to a battery and/or a system load. When the input terminal BUS is connected to an external circuit instead of an external power source, the bi-directional switching regulator becomes a buck switching regulator operating under a power supply mode. That is, the same circuit shown in FIG. 1 will operate to convert a higher battery voltage VBAT from the battery BAT to a lower input voltage VBUS through the power stage 11 and supplies power to the external circuit connected to the input terminal BUS. Generally, a current control switch will be provided between the output terminal SYS and the battery BAT.
The power stage 11 includes an upper-gate switch S2, a lower-gate switch S3 and an inductor L, all of which are connected to a common switching node LX. Under the charging mode, a current supplied from the external power source will flow toward the output terminal SYS through the inductor L and the upper-gate switch S2. This conventional bi-directional switching regulator 10 is not suitable for the application where the output terminal SYS acts as an USB port, because the charges injected by hot plug-in may damage the battery. And, if the battery voltage VBAT is too low, the level of the output voltage VSYS will also be affected, which may cause the system load to be unable to operate normally. Besides, under the circumstance where the battery BAT is not connected, if the battery terminal (the node where the battery voltage VBAT is) is short-circuited, the power stage 11 will keep operating to supply current to the battery terminal, causing serious problems to crash the bi-directional switching regulator 10 and to damage the circuit. And, if a voltage difference between the output voltage VSYS and the battery voltage VBAT is too large, there will be high power consumption; on the other hand, if there is no voltage difference between the output voltage VSYS and the battery voltage VBAT, the battery BAT cannot be charged effectively.
In view of the above, to overcome the drawbacks in the prior art, the present invention proposes a bi-directional switching regulator and a control circuit of the bi-directional switching regulator which are capable of effectively controlling the charging current to prevent the switching regulator from being crashed and the battery from being damaged.